If Spock's head was turned, how would he know who dropped the hammer?
Maybe he would use logic to conclude that it was the guy who immediately picked up the hammer, threw it into the closet, ran out the door and down to the officers' mess and grabbed a Dr. Klingon (a popular soft drink) to look cool and avoid suspicion, then ran toward the escape deck killing a Vulcan security guard on the way, then ran into the virtual reality theater (without paying) and finally tried to shoot the security guards when placed under arrest.